In the operation of aircraft, it is important that the crew be able to determine whether movable portions of the aircraft structure are in proper positions. For example, there is a need to verify that the translating thrust reverser cowls are in their proper lock positions when the thrust reversers are not in use. The required indication of the lock position is currently provided by a proximity sensor mounted on a fixed structure, such as the nacelle torque box. A target is fixedly mounted on the translating cowl opposite the sensor. The sensor generates a signal when the target is within a predetermined distance of the sensor. An electrical circuit transmits the signal and converts it into a visual indication in the cockpit that the cowl is in a locked position.
A number of problems have been encountered in connection with the use of known sensor arrangements in lock indicating systems for thrust reverser translating cowls. The sensors are designed to be always separated from the target by a gap. A correct gap dimension when the cowl is in its lock position is critical to the proper functioning of the indicating system. A gap that is too large results in a false indication that the cowl is not in a lock position. Such false indications in turn cause expensive and unnecessary flight delays. A gap that is too small can result in undesirable contact between the delicate sensor and the target and even damage to the sensor when it is impacted by the target.
In current systems, the sensor is mounted in a fixed position on a fixed structure and then the target is mounted on the cowl. The mounting of the target is adjustable to preset the critical gap dimension. The presetting of the gap dimension is difficult and tedious in installations such as the thrust reverser translating cowl on the Boeing 737-300 aircraft. The adjustment has to be made blind because the sensor is mounted on the edge of the fixed structure, and the end of the cowl forms a flange which overlaps the fixed structure. Thus, when the cowl is in its lock position, the sensor and target are not accessible from either the inside or the outside. Therefore, adjustment of the gap has to be accomplished by a trial and error method. One such method is to place putty between the sensor and the target, close the cowl, open the cowl, measure the thickness of the putty compressed between the sensor and the target, and make any required adjustments by shimming the target. Another method is to use the visual indicator of the lock indicating system to determine when the gap has been adjusted to its desired dimension. Such trial and error methods of adjusting the target position are time consuming and therefore expensive and do not have a high degree of accuracy. In addition, the arrangement of a fixed preset target position does not have any means for compensating for minor differences in the position of the cowl when it is in its lock position. These factors can combine to produce false open indications or damage to the sensor under flight conditions.
Th patent literature includes a variety of examples of systems for indicating the relative position of a structure. U.S. Pat. No. 2,819,359, granted Jan. 7, 1958, to J. P. Johnson, discloses a warning device for indicating relative movement between two adjacent structures. A cylindrical housing is mounted on one of the structures, and a rod is mounted on the other structure. When relative lateral or longitudinal movement between the structures exceeds a safe limit, the end of the rod which projects into the open end of the housing contacts the inner surface of the housing sidewall. This closes a circuit to set off an alarm. A cylindrical rubber "boot" or sleeve surrounds the rod and sealingly engages the outside of the housing to keep moisture, dirt, etc. out of the assembly.
U.S. Pat. No. 3,436,726, granted Apr. 1, 1969, to A. O. Dentz, discloses a warning device to indicate that a vehicle hood is not fully closed. In one embodiment, a plunger mounted on the vehicle contacts the hood. The plunger extends when the hood opens to close a circuit and set off an alarm. In another embodiment, a disk is slidably mounted in a cylinder attached to the hood. When the hood opens, a safety latch hook carried by the vehicle contacts the disk and slides it down into the cylinder to move two contacts together and complete an electrical circuit.
U.S. Pat. No. 3,454,869, granted July 8, 1969, to B. Strauss et al., discloses a proximity sensing system for use in an aircraft environment. The system is responsive to changes in inductance caused by changes in the separation between a sensor and a positionable target. Strauss et al. state that it is desirable to have a relatively large gap between the sensor and the target.
U.S. Pat. No. 3,710,370, granted Jan. 9, 1973, to A. P. Quilici, discloses a warning system for indicating improper coupling of a trailer hitch to an automobile. A top portion of the coupler ball carried by the automobile is spring biased away from the main body portion of the ball. When the ball socket hitch member is properly coupled to the ball, the socket moves the top portion of the ball toward the main body against the action of the spring to close the circuit and de-energize an alarm.
U.S. Pat. No. 4,058,792, granted Nov. 15, 1977, to J. A. Soltesz, discloses a system for detecting changes in the orientation of a floating structure, such as a boat. The system includes a submersible sensor having two weighted portions. Each of the portions carries a switch, and the two switches are normally in contact with each other. A change in orientation causes separation of the switches.
U.S. Pat. No. 3,876,977, granted Apr. 8, 1975, to W. Ladewig, discloses a proximity switch for an automobile horn. U.S. Pat. No. Re. 28,590, reissued on Oct. 28, 1975, to M. I. Salmi, discloses an indicating apparatus for use in coupling a trailer to a vehicle The apparatus senses and indicates deflection of a guide line and the distance between the trailer and the vehicle. U.S. Pat. No. 4,127,856, granted Nov. 28, 1978, to G. G. Bickel, discloses a latch on a loading dock to engage a rod carried by a truck. The latch has indicator switches that are activated by arms of the locking mechanism contacting buttons on the switches.
The above patents and the prior art discussed and/or cited therein should be carefully considered for the purpose of putting the present invention into proper perspective relative to the prior art.